The present invention relates generally to an engine monitoring system and more particularly to a device for sensing fuel line injection characteristics.
Analyzing the performance of engines which employ fuel injection, particularly diesel engines, requires an indication of the timing, as well as waveform information, such as the pulse width of pressure pulsations in the fuel injection lines. Various sensor systems have been devised for attachment to or within the injection line to provide a signal indicative of the pulsations. Some require the fuel line to be broken so the sensor can be placed in direct communication with the line. Typical of such previous devices is a diaphragm deflected by the fuel pressure wave to cause a resistive change in a transducer. A device of this type cannot be quickly and easily moved from line to line, is subject to continuous wear from fuel flow, and requires machined fittings which are expensive to manufacture. Different couplings are necessary to accommodate injection lines of various sizes.
Other devices utilize a piezoelectric transducer coupled to a fuel line to provide an output which varies with the radial expansion of the fuel line. These devices are expensive and often are easily damaged in the hostile environment to which they are subjected. Such devices are not only fragile but also are difficult to connect to the line. For proper repeatability of measurements, the piezoelectric-type transducer has to be engaged with the line using sufficient pressure for coupling. However, too much pressure can damage the transducer. Difficulty arises when trying to clamp the device properly when there is little working space around the engine under test, making connecting and preliminary adjustment of the transducer very time consuming.
Pressure sensitive transducers encased between a housing and the fuel line have also been used to monitor fuel injection. The housing must be rigidly attached to the line and requires either a permanent installation on the line or the bolting of split halves around the line. Such a device is not readily adaptable to different sized lines and cannot be quickly connected for use, especially where working space around the lines is limited.
Typical of other previous devices are transducers which are mounted permanently on the engine near the fuel injection nozzle. Since the transducers remain on the engine, they are subject to continuous abuse while the engine is operating. A separate transducer and its associated mounting hardware are necessary for each cylinder, multiplying the cost of the test system.
Although various transducer devices have heretofore been utilized to monitor fuel line injection, none have proved to be entirely satisfactory. Coupling the transducer to the line has been too time consuming especially where space is limited. Most are not adapted for easily and quickly moving the device from one line to another, particularly where there is a change in line diameter, and most do not hve self-adjusting or self-compensating features. Piezoelectric-type transducers are often used, and they are expensive and easily damaged. They tend to have a short lifetime when used in the environment of an engine diagnostic system.